The family of Joan Rivers has thanked everyone for the "outpouring of love and support" after the comedian was reported to be in a "critical condition" in hospital.

An update on the 81-year-old star's condition will be provided "as it becomes available", spokesman Sid Dinsay for the Mount Sinai Hospital in New York said.

In a statement, he said: "This morning, Joan Rivers was taken to the Mount Sinai Hospital in New York, where she is being attended to.

"Her family wants to thank everybody for their outpouring of love and support. We will provide an update on her condition as it becomes available."

Earlier, a spokesman for the NYPD said: "An 81-year-old is in a critical condition at Mount Sinai Hospital."

He was unable to confirm reports on the TMZ website that her heart had stopped beating at one point.

The US site is reporting that Rivers was undergoing a throat procedure in a clinic when she became unwell but the spokesman could not confirm this.

He said the emergency call was made at 9.39am local time from an address in East 93rd Street, Yorkville, where there is an outpatient centre which describes its mission as to "serve as a community resource for digestive disorders".

Stars have been taking to Twitter to send their best wishes to the comedian.

Heroes star Zachary Quinto tweeted: "sending so much love and healing energy to @Joan_Rivers !!! no one is ready to go on without you lady!!!"

Modern Family actor Jesse Tyler Ferguson wrote: "Sending all my love and prayers to my friend @Joan_Rivers right now."

While actress Marlee Matlin tweeted: "Get well @Joan_Rivers! And moon the doctors for us while you're recuperating!".

American TV host Billy Bush wrote on his Facebook page that Rivers' daughter Melissa had told him to "please pray".

He wrote: "Praying for Joan Rivers who is in critical condition at Mt Sinai hospital in NY. Texted with Melissa Rivers who said "please pray". Already doing that. Joan is beloved around here.

"A regular guest on Access Hollywood Live she never fails to deliver. She taped her post Emmy special Tuesday in LA and was strong. This is out of nowhere. Come on Joan you have to make it. Just think of all the material. Sending love and prayers."

Actress Kelly Ripa tweeted: "Praying for the great @Joan_Rivers one of the true loves of my life."